Apparatus for temperature control of chemical reaction vessels



April. 9, 1957 A. BREMER ET AL. E 2,788,264

APPARATUS ROR TEMPERATURE CONTROIJ OR CHEMICAL REACTION vEssEEs Filed May 25, 195s s sheets-snee: '1

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E. 6. Hohmann P. R.' H091 5. VH. M

April 9, 1957 A. BRI-:MER ET AL 2,788,264

APPARATUS FOR TEMPERATURE CONTROL OF CHEMICAL REACTION VESSELS Filed May 25, 1953 5 Sheets-Sheet 2 coNTRoLLER l l l l s l l a l l NL: l

`l l l l RATIO CONTROLLER TEMPERATURE CONTROLLER Nea April 9, 1957 A. BREMER ET AL 2,788,254

APPARATUS POR TEMPERATURE CONTROL OF CHEMICAL REACTION VESSELS Filed May 25, 1953 3 Sheets-Shea?l 3 24 Y '25 HEAT V ExcHANeER 22 Y L L A sa 55 se pas rg y W 22m 49 4 i 2%\xv l r 1 REACTOR /5o l /25 542 I Y Rimesamon Fig. 5

\nven1'ors: A Bran-mr E6. Holzmann I P. RHOLJT ENt H744 Q Thair Agrzr' United@ States Pafeif "0 APPARATUS FR TEMPERATURE CGNTROL 0F CHEMICAL REACTION VESSELS Application May 25, 1953, Serial No. 357,304

6 Claims. (Cl. 23--284) This invention relates to a method and apparatus for controlling the temperature of a chemical reaction vessel and pertains moreparticularly to the control of an exothermic reaction in a chemical reaction vessel at a substantially constant temperature by a circulating heat exchange medium, the temperatureV of which may be varied over a wide range.

Circulation of a liquid heat exchange medium through a coil or jacket or over the external surface of a container or vessel has long been used as a method of controlling the temperature of vessels containing liquids or solutions of solids in liquids, chemical reagents which either absorb or evolve heat in the process of reaction, etc. The problem of controlling the temperature of chemical reactions, however, in which the amount of heat absorbed or evolved varies within wide limits during the course of the reaction, has usually involved the useof large volumes of heat exchange medium entailing considerable expense.

,In 4many chemical reactions, it is absolutely essential that .the reaction temperature be controlled within very narrow limits of an order such as il F. For exam ample, polyvinyl chloride may be manufactured by the suspension process of batch polymerization of vinyll chloride in methanol-Water solution to produce a granular polymer with lgood electrical and mechanical properties. The properties are closely related to the molecular weight of the polymer, which, in turn, depends critically on the temperature at which the reaction takes place.

It has been found that best results are obtained in manufacturing polyvinyl chloride when lthe reaction is carried out at 122 F. Very close control of the temperatureis required to produce a polymer with a narrow range-of molecular weights. The entireI charge; for each bath is pumped into a jacketed, glass-lined pressure ves* sel, and adequate agitation is provided during the reaction so as to minimize ltemperature differences in various parts of the batch. In order to obtain a product with the desired properties it is necessary to control variationscf temperature within the specied .liinits'of il F. of the optimum chosen reaction'temperature.v

It is, therefore, an object of this invention to' provide a temperature control system for controlling automatically the heating and cooling operations of chemical reaction vessels.

A further object of this invention is'ito provide a temupstream and downstream of the mixing point 26. The

perature control system for chemical reaction vessels,- said system comprising a closed circuit for continuously` circulating the heat transfer liquid therein and animproved arrangement for selectively heating j and/orwcoolf,

perature, or within a very narrow temperature range, say, il F. of the desired reaction temperature.

These and other objects of this invention will be understood from the following description taken with reference to the attached drawing, wherein:

Figures l and 2 are schematic liow diagrams showing the arrangement of the principal components of the present system connected to a chemical reaction vessel.

Figure 3 is a schematic ow diagram showing the prin cipal components of the present temperature control system connected to a plurality' of chemical reactors such as shown in Figures l and 2.

Referring to Figure l of the drawing, the proposed temperature control system is illustrated as being mounted y adjacent a chemical reactor or reaction vessel 11 surrounded by a water jacket 12 in which cooling water may be circulated from a conduit 13. ln order to insure maximum circulation within the jacket 12, the inlet uid conduit 13 may be provided with a series of injector noz zles diagrammatically represented-as 14, 15 and 16.

The intake of a pump 17 for circulating the heat transfer fluid through the presenttemperature control system is in communication with the discharge conduit 1S from the jacket 12. The discharge conduit 2t) from the pump 17 branches at a T-connection 21 to form two loops in the closed circulating system. One loop, the heating loop, comprises conduit 22, valve 23, heater 24, and conduit 25' which connects at point 26 to the inlet conduit 13 leading back to the jacket 12. The second or cooling loop in the system comprises a flow control valve 2S, conduit Z9, refrigerator 'unit 3i) and conduit 31 which connects with the inlet conduit 13 to the jacket 12 .through a three-way valve 32. The cooling loop is also provided with a by-pass conduit 33 whichl connectsl conduit 29 through the three-way valve 32 with conduit 13, thus eitectvely by-passing the refrigerator unit 3i). v

The circulating stream in the closed syste-m may split at 4point 21 and recombine4 at point 26. The mixing' point 26 is preferably as close to the inlet of the tank jacket 12 as possible, so as to 'reduce the residence time 'either pneumatically, hydraulically or electrically. The

control valves 35 and 37 in the inlet line to the heater 24 are actuated by a temperature controller 33 whichl has a temperature tap 39 in conduit 13 downstream from 4,the mixing point 26 and a second-temperature tap itl lin conduit 25 between the heater 24 and the mixing point 26. The three-way mixing valve 32 in conduit 31 is actuated by, a second temperature'-controller 42 having temperature taps 43 and 44 in conduit 13, respectively,

controllers 38 and 42 may be differential temperature controllers, for example, the"Dynalog' controller manu-v desfibed in' factured by the Foxboro Company, v. and their `Bulletin No.427-l,iAugust 1950.

Valve23jis`actuated by a temperature controller 46 whichv has .onetemperature tap 427 in conduit 13 at the point where it enters the jacket 12 of thel reaction' vessel.

The temperature controller 4o is also connected to a temperature measuring device, for example, a resistance thermometer 4S built into the reaction vessel i1. PreferV ably, vthe sensitive resistance'thermometer 48 'is "com Patented Apr. 9, 1957` The valves used in the entire' S nect'ed toa high-,gain controller 49 which is responsive thereto and transmits an error signal to the temperature controller 46. Alternatively, the temperature measuring device 4S may be of the pressure-bulb type with rate action such as Taylor Instrument Companies Transaire Temperature Transmitter' Model 317RG, p. l0, Bulletin 98097, April 1951. If a unit i3 of this type were employed, the controllers datand 49 could be Taylor Tri- Act pneumatic controllers No. 329 RFlll as shown on page 4 of the same bulletin. ln order that a constant flow be maintained through the system, the control valve 28 is connected to a flow controller 51 having pressure taps 52 and 52a. upstream and downstream of an orice 53 positioned in conduit 2t) upstream of point 21 where the circulating stream divides. The flow controller 51 may be of any suitable design. For example, it may cornprise a differential pressure cell for measuring differential pressure across the orice S3 together with pneumatic controller'such as type IVI-5ft manufactured by Foxboro Company and shown in their Bulletin No. 463, March 1952.

If desired, the system may be provided with a tank or expansion chamber' 54 in communication withv the suction side of the pump 17 to provide storage as the volume of the heat transfer medium in the system expands or contracts during the reaction cycle and to make up for leakage losses.

Any suitable liquid may be used as the heat exchange medium. Water, alcohol, glycerine, glycol or mixtures thereof, oil,v a mixture of diphenyl and diphenyl ether o known as Dowtherm, and other similar materials, especially those with high specific heats, are all satisfactory. The most convenient and least expensive medium for temperatures below 100 C., of course, is Water and the operation of the present system will be described as using water for the heat exchange medium.

The temperature control system shown in Figure-2 of the drawing differs from that illustrated in Figure l in two respects. There are many ways of maintaining a constant flow throughout the system and apportioning the flow between the heating and cooling loops of the system at a certain ratio. In the system illustrated in Figure-2 a ratio controller 57 is inserted in the system to receive signals from the temperature controller. 46 and to transmit in response thereto actuating signals to the control valves 23 and 2S to open or close said valves to a greater or lesser degree thereby controlling the ratio of fluid being circulated in the hot and cold loops of the system. Additionally, a by-pass line 58 is provided around the heater 24 and connects with a three-way valve 59 in the conduit line 25 leading from the heater 24. The three-way mixing valve S is actuated by a temperature controller 60 which is similar to temperature controller 4t2 which actuates valve 32 in the cooling loop of the system. Thus, in Figure 2, the heater 2,4 is maintained at a substantially constant temperature and the temperature of the hot loop stream is controlled by mixing at valve 59 the fluid flowing from the heater 24A through conduit 25u/ith a oW through by-pass conduit 58.

Figure 3 shows a series of temperature control systems (each similar to that illustrated in-Figure l) for several reactors 11 and 11a which are connected in parallel-tov the same heat exchanger 24 and refrigerationunit 30. It is realized that additional units orreaction-vessels may also be connected in parallel to the same heat-exchanger and refrigeration unitdepending upon the chemical reaction carried out in the reactors and the peak loads required from the heat exchanger and the refrigeration unit. In the manufacture of polyvinyl chloride by the suspension process of batch polymerization of vinyl chloride in methanol-water solution, the individual peak loads of `the-differentl reactors 11 and 11a (and others) can be staggered andthe designed capacity of the refrigera- 4. tion unit can be based on the average load rather than on the sum of all the peak-loads.

All automatic controllers referred to hereinabove are preferably of commercially available types well known to the art.

ln operation, the reaction takes place in the reaction Vessel il (Figure l) whose temperature depends, first, upon the heat generated or required by the reaction, and second, on the heat removed or added by the cooling water, since losses through the body of the vessel-and may be consiedered negligible. In order to maintain a constant temperature throughout the reaction, the heat absorbed by the cooling water must be equal to the heat generated by the reaction at every instance. The' present system is capable of doing this and iii Y satisfies the desired limitation-of *:l F. of permissible temperature variation.

The temperature 0i of the coolingwater entering the jacket 12 is the controlling factor in determining the rate at which heatis transferred'through the jacket walls.

The heat added to or removed from-the cooling Water circulating the water at a high flow rate m.

Since good control of the temperature within thereaction vessel 11 is achieved only if the jacket inlet water temperature 0i can be instantaneously changed to a temperatureV either higher or lower than the average temperature called for by the reaction rate, the present system provides means for mixing two streams of uid, one hot (mil), the other cold (mgz) at avpoint 26 close to the jacket intake. The steam of fluid coming out of the discharge jacket conduit 13 passes through the pump 17 and conduit 20 to be split at point 21, a portion of the flow (m1)` passing down conduit 22` through the heater 24 while the otherportion of the ow (m2) passes through conduit 291and refrigerator 3tl`or through bypass conduit 33. The ratio of these two streams is controlled by the temperature recorder-controller 46 Which'actuat'es control valve 23 to determine the amount of liuid ilow through the'hot loop of the system, while theV control valve-.28 isactuated by ow controller 51 to maintain the total owthr'ough the system constant and allow theother portion of the total stream to pass throughthe'cold loop of the system. A ilowy controller is employed since' resistance to the llow of circulating tluid varies in the system depending upon the ratio of the two streams passing through the hot and cold loops of-the'system. The streams passing through the hot and cold loops of thesystem mix at point 26, and the mixed stream-temperature 0, at the jacketV inlet is a function of the ilowfoffratiofmi/'nia and of the hot and cold stream temperatures 01`and 02.

In order toV operatel the present system economically with a' minimumaverage load on the refrigeration unit 30,- it is'desirable that the lows m1 and m2 through the hot and cold loops,.respectively, be kept equal. in order to accomplish this: it; is-.neee'ssaryV that the' temperatures A1= (01x-t2) and'` @zwi-02) be, kept equal'. Thus, the' temperature difference between the hot stream (i1 in conduit 2,5 andthe mixed hot and cold stream 0i in conduit 13 must equal the temperature difference between the mixed hot andcold stream 0i in conduit 13 and the temperature of the cold, stream @2in conduit 31. Thus,the present systemprovidesan arrangement whereby a hot and a cold stream coming from conduits 2.5 and 31 may be mixed at a point-26Qwith the resulting stream passingl through Conduit 13 andlinto the jacket 12 having a. temperature half-way between thetemperatures of the hot and cold streams when the flow-rates of the-'two streams areequal. Foifexample, if it is desired to operatel the reaction at122 F. ana during para of the` Cycle -of the, i' exothermic'reaction the temperature of the cooling water entering the jacket l2 through conduit t3 is 70 F., the' temperature 91 of thewater coming from heater 24 isf preferably maintained at 73 F. while the temperature of 62 coming from the refrigerator unit 30 is kept at 67 F. The two streams would lbe mixed at point 26 to give a mixed temperature stream 0i of 70 as demanded by the temperature controller 4d. The temperature controllers 38 and 42 are provided for maintaining the temperatures of the `streams coming from the heaterA and refrigerator loops at any desired temperature, but are preferably set to maintain the temperatures of the two streams the same number of degrees respectively 'above and below the temperature li of the mixed stream in conduit 13 after the two streams pass the mixing point 26.

The temperature controller 3S is set to control Ithe temperature of the stream passing through the hot loop at a predetermined number of degrees, say, 3 F., above the temperature entering the jacket i2 from conduit i3. The temperature `of the fluid in the two conduits 25 and i3 is sensed by the temperature taps 4th and 39, respectively. lf, for example, the indicated temperature between the two points drops 4below the preset ditference of three degrees which -is desired, 'the error signal from the temperature controller 3S will either lopen or close the control valves 3S and 37 in the `steam and cold water lines as needed. Heat will 'be supplied to the heater 24 to a greater or lesser degree in order to again reestablish a three-degree temperature difference `between flow streams in conduits 25 and 13.

ln a like manner, the temperature rcontroller 42 acts to maintain the temperature 0, of the how stream in conduit 3l at three degrees Ibelow the mixing point 26. While the temperature controller 42 could be used to control the temperature of the `refrigeration unit 3i) it has been found to be more economical to run the refrigeration unit at a hxed value, putting a portion of the flow passing through the cold loop through the refrigeration unit while the other portion of the flow passing through the cold loop is roy-passed through conduit 33 and `again mixed with the tlow from the refrigeration unit Vby valve 32 which is controlled by the temperature controller 42. Thus, the temperature controller 42 controls the mixing ratio of the two streams of conduits 31 and 33 to maintain a temperature 6, on reaching mixing point 26 which is three degrees below that of the desired temperature in conduit 13.

The mixing ratio `of the two streams through the hot and cold loops of the system, which mix at point 26, is controlled by the control valve 23 which is 'actuated by temperature controller 46. The set point of the temperature controller 46 is made dependent on the reaction rate by the high-gain controller 49 which is actuated from the lsensitive resistance thermometer 48 in the vessel l1. A set point in the controller 49 is previously set at the temperature at which it is desired to carry out the reaction in vessel ll. As the reaction rate increases, the temperature 6r of the reaction mixture also tends to increase. This error is amplihed in controller@ which transmits a signal to and lowers the set point of temperature controller 46. This change of set point in temperature controller 46 causes it to transmit a signal to actuate valve 23 which rdecreases the how ratio ml/m2 until the jacket intake temperature 9i is equal to the new set point ofthe temperature controller 46. Due to the lowering of the temperature 0i of the water entering the jacket 12 of the vessel il, the temperature controllers 33 and 42 are called upon to lower also the temperatures 6, and 49Z of the hot and cold streams, respectively, in order to restore the dilerences A, and A, to equilibrium. As equilibrium is again approached, the flow ratio Inl/mZ returns to unity.

In Figure l the stream of fluid passing through the hot loop of the system is maintained at a temperature A, above t?, by controlling the tlow rate and temperature of 6 the heating medium through conduit 34 to heat exchanger 24 so that the desired temperature 0,:(0rj-A1) of stream m1 is obtained. The heating medium -in one `system con-A sists of a mixture of water at 87 F. and low-pressure t steam. The control action of temperature controller -33 is sequenced so as to minimize the steam consumption. During those parts of the reaction cycle when the jacket outlet w-ater temperature 00 exceeds the desired hot stream temperature 01, the heating water ow to the heat exchanger 24 is stopped completely to prevent unnecessary loading of the cooling system. l

The same results yare obtain xby an alternative method as shown in Figure 2 of the drawing. Here the heat exchanger Z4 is controlled to produce in conduit 25 a constant high downstream temperature of, say,

The desired hot -stream temperature, 0 is obtained 'by mixing water from the heater 24 with water that has ybypassed the heater through conduit 58 and is 'at the tem-l perature 00 of the jacket outlet. The flow ratio of the two `streams from the heater 24 and through by-pass line 53 is controlled by valve 59 and temperature controller 60 to maintain a constant temperature difference Ar: (0i-0,5)

The design of the heating loop illustrated in Figure 2 has the advantage that it may be readily adapted to` parallel operation of a number of similar reaction control systems, employing a common heat exchanger 24 as shown in Figure 3 of the drawing. Normally, a plurality of reaction vessels 11 and 11a would only be connected in parallel when the reaction being carried out therein was of such a character that its time cycle demanded large amounts of heating or cooling capacity for portions of the cycle with no demand for any heating or cooling capacity in other portions of the cycle. Thus, in the batch polymerization of vinyl chloride, which has been considered, at least two reaction vessels 1l and 11a could ponents of the system shown in Figure 3 are identical to,

and hence numbered the same as, corresponding units in Figures 1 and 2. The above-described parallel arrangement of a series of reactors having a common heating and refrigeration unit is also desirable where the nature of the product being produced necessitates the removal of a reactor from service every few batches for cleaning purposes.

Thus, it may be seen that the present temperature control system provides a closed system having two loops, a heating loop and a cooling loop, for circulating a heat exchange medium from the cooling jacket of a reaction vessel, and back to the vessel.` A portion of the efiluent, stream from the jacket is cooled to a few degrees belowv the water temperature being injected into the jacket' and the other portion of the stream is heated to a few degrees above the desired temperature of the water entering the jacket, thereby providing means for accurately controlling the temperatureV of reaction in the vessel at all times and by allowing the reaction to run away with itself. Thus,'

at critical points of the reaction, for example, when it is desired to speed the reaction, or when the temperature starts to diminish for some reason, it becomes necessary.l to let the temperature go up` under its generated heat.

Thus, it may be seen that only by employing the present arcanes' s temperature control systeml is it possible to maintain a reaction temperature within the required limits ofsay ztl" F. throughout the reaction to` obtain a good product.

While in the above description the reaction vessel .lil has been described as having a waterjacltet l2, it is realized that other means of cooling the vessel may be employed. Since various means, such as cooling coils within the vessel or sprays outside the vessel, are well known to the art and constitute no part of this invention, they will not bedescribed in further detail here.

We claim as our invention:

1. A system for carrying out chemical reactions at a substantially constant temperature, said system coi prising a reaction vessel, said vessel being provided with heat exchange means having fluid inlet and outlet means, conduit means connected between Said inlet and outlet means to .form a closed external circuit for circulating heat exchange fluid in said heat exchange means, flow control means in said conduit means for maintaining the flow rate therethrough at a constant value, a pump in said conduit means for forcing a fluid therethrough, said conduit means comprising two conduit loops in parallel, each of said loops comprising a closed hydraulic circuit, means for heating the heat exchange fluid in one of said means for cooling the heat exchange fluid in another of said loops, means in said conduit means responsive to the temperature in the reaction vessel for controlling the flow ratio in said parallel loops, and control means responsive to the temperature of the fluid in said conduit means for maintaining the fluid circulating in the heating and cooling loops at predetermined temperature values respectively above and below the temperattu-e the fluid entering the heat exchange means the vessel.

2. A system for carrying out chemical reactions at a substantially constant temperature, said system comprising a reaction vessel, said vessel being provided with heat exchange means having fluid inlet and outlet means, conduit r c ns connected between said inlet and outlet means to form closed external circuit for circulating heat exchange fluid in said heat exchange means, flow control means in said conduit ment for maintaining the flow rate therethrough at a constant value, a. pump in said conduit means for forcing a fluid therethrough, said conduit means comprising two conduit loops in parallel which join at a mixing point adjacent said fluid inlet means of the heat exchange means, whereby the fluid streams flowing through said conduit loops are mixed at said mixing point, each of said loops comprising a closed hydraulic circuit, means for heating the heat exchange fluid in one of said loops, means for cooling the heat exchange fluid in another of said loops, valve means in said conduit means for controlling the flow ratio in said parallel loops, controller means responsive to the temperatures of said reaction vessel and of said duid entering the inlet means of said heat exchange means for actuating said valve means, and control means for maintaining the fluid circulating in the heating and cooling loops at predetermined temperature values respectively above and below the temperature ot' the fluid entering the heat exchange means of the vessel. i

3. A system for carrying out chemical reactions at a substantially constant temperature, said system compris Aing a reaction vessel, said vessel being provided with heat exchange means having fluid inlet and outlet means, conduit means connected between said inlet and outlet means to form a closed external circuit for circulating heat exchange fluid in Asaid heat exchange means, flow control means in said conduit means for maintaining the flow rate therethrough at a constant value, a pump lin said conduit means for forcing a fluid therethrough, said conduit means comprising two conduit loops in parallel which join at a mixing point adjacent said fluid inlet means of the'heat exchange means, whereby the fluid streams flow- Sil ing through said conduit loops are mixed at said mixing point, each of said loops comprising a closed hydraulic circuit, heater means in one of said loops for heatmg the heat exchange fluid, refrigerator means in the other of said loops for cooling the heat exchange fluid, valve means in said conduit means for controlling the flow ratio in said parallel loops, controller means responsive to the temperatures of said reaction vessel and of said fluid entering the inlet means of said heat exchange means for lactuating said valve means, by-pass conduit means in said other conduit loop for bypassing said refrigerator means, and control means for maintaining the fluid circulating in the heating and cooling loops at predetermined temperature values respectively above and below the temperature of the fluid entering the heat exchange means of the vessel.

4. A system for carrying out chemical reactions at a substantially constant temperature, said system comprising a reaction vessel, said vessel being provided with heat exchange means having fluid inlet and outlet means, conduit means connected between said inlet and outlet means to form a closed external circuit for circulating heat exchange fluid in said heat exchange means, flow Control means in said conduit means for maintaining the flow rate therethrough at a constant value, a pump in said conduit means for forcing a fluid therethrough, said conduit means comprising two conduit loops in parallel which join at a mixing point adjacent said fluid inlet means of the heat exchange means, whereby the fluid streams flowing through said conduit loops are mixed at said mixing point, each of said loops comprising a closed hydraulic circuit, heater means for heating the heat exchange fluid in one of said loops, refrigerator means for cooling the heat exchange fluid in the other of said loops, first valve means in said conduit means for controlling the flow ratio in said parallel loops, controller means responsive to the temperatures of said reaction vessel and of said fluid entering the inlet means of said heat exchange means for actuating said first valve means, first temperature controllermeans responsive to the differential temperature of the flow streams downstream of said heater means and downstream of said mixing point for controlling the temperature of said heater means, by-pass conduit means in said other conduit loop for by-passing said refrigerator means, second valve means in said cooling loop downstream of said refrigerator means for controlling the flow ratio of the streams flowing through and by-passing said refrigerator means, and second temperature controller means responsive to the diflerential temperature of the flow stream in said cooling loop downstream of said second valve means and downstream of said mixing point for actuating said second valve means, whereby the fluid circulating in the heating and cooling loops is maintained at predetermined temperature values respectively above and below the temperature of the fluid entering the heat exchange means of the vessel.

5. A system for carrying out chemical reactions at a substantially constant temperature, said system comprising a reaction vessel, said vessel being provided with heat exchange means having fluid inlet and outlet means, conduit means connected between said inlet and outlet means to form a closed external circuit for circulating heat ex change fluid in said heat exchange means, flow control means in said conduit means for maintaining the llow rate therethrough at a constant value, a pump in said conduit means for forcing a fluid therethrough, said conduit means comprising two conduit loops in parallel which join at a mixing point adjacent said` fluid inlet means of the heat exchange means, whereby the fluid streams flowing through said conduit loops are mixed at said mixing point, each of said loops comprising a closed hydraulic circuit, heater means for heating the heat exchange fluid in one of said loops, refrigerator means for cooling the heat exchange fluid in the other of said loops, valve means in said conduit means for controlling the flow ratio in said parallel loops, controller means responsive to the temperatures of said reaction vessel and of said fluid entering the inlet means of said heat exchange means for actuating said valve means, first by-pass conduit means in one of said loops for by-passing said heater means, second by-pass conduit means in said other loop for bypassing said refrigerator means, and control means for maintaining the iluid circulating in the heating and cooling loops at predetermined temperature values respectively above and below the temperature of the tluid entering the heat exchange means of the vessel.

6. A system for carrying out chemical reactions at a substantially constant temperature, said system comprising a reaction vessel, said vessel being provided with heat exchange means having fluid inlet and outlet means, conduit means connected between said inlet yand outlet means -to form a closed external circuit for circulating heat exchange uid in said heat exchange means, flow control means in said conduit means for maintaining the ow rate therethrough at a constant value, a pump in said conduit means for forcing a tluid therethrough, said conduit means comprising two conduit loops in parallel which join at a mixing pointadjacent said uid inlet means of the heat exchange means, whereby the fluid streams owing through said conduit loops are mixed at said mixing point, each of said loops comprising a closed hydraulic circuit, heater means for heating the heat exchange fluid in one of said loops, refrigerator means for cooling the heat exchange fluid in the other of said loops, valve means in said conduit means for controlling the flow ratio in said parallel loops, controller means responsive to the temperatures of said reaction vessel and of said fluid entering the inlet means of said heat exchange means for actuating said valve means, rst by-pass conduit means in one of said loops for by-passing said heater means, second by-pass conduit means in said other loop for by-passing said refrigerator means, iirst control means in said heating loop for controlling the iow ratio of the streams owing through and by-passing said heater means, and second control means in said cooling loop for controlling the ow ratio of the streams flowing through and by-passing said refrigerator means, whereby the fluid circulating in the heating and cooling loops is maintained at predetermined temperature values respectively above and below the temperature of the uid entering the heat exchange means of the vessel.

References Cited in the le of this patent UNITED STATES PATENTS 1,382,569 Tait June 21, 1921 2,104,333 Rosenblad Ian. 4, 1938 2,217,703 Pew et al. Oct. 15, 1940 2,371,381 Campbell et al Mar. 13, 1945 2,448,538 Mason Sept. 7, 1948 FOREIGN PATENTS 709,445 France Aug. 6, 1931 

1. A SYSTEM FOR CARRING OUT CHEMICAL REACTIONS AT A SUBSTANTIALLY CONSTANT TEMPERATURE, SAID SYSTEM COMPRISING A REACTION VESSEL, SAID VESSEL BEING PROVIDED WITH HEAT EXCHANGE MEANS HAVING FLUID INLET AND OUTLET MEANS, CONDUIT MEANS CONNECTED BETWEEN SAID INLET AND OUTLET MEANS TO FORM A CLOSED EXTERNAL CIRCUIT FOR CIRCULATING HEAT EXCHANGE FLUID IN SAID HEAT EXCHANGE MEANS, FLOW CONTROL MEANS IN SAID CONDUIT MEANS FOR MAINTAINING THE FLOW RATE THERETHROUGH AT A CONSTANT VALUE, A PUMP IN SAID CONDUIT MEANS FOR FORCING A FLUID THERETHROUGH, SAID CONDUIT MEANS COMPRISING TWO CONDUIT LOOPS IN PARALLEL, EACH OF SAID LOOPS COMPRISING A CLOSED HYDRAULIC CIRCUIT, MEANS FOR HEATING THE HEAT EXCHANGE FLUID IN ONE OF SAID LOOPS, MEANS FOR COOLING THE HEAT EXCHANGE FLUID IN ANOTHER OF SAID LOOPS, MEANS IN SAID CONDUIT MEANS RESPONSIVE OF THE TEMPERATURE IN THE REACTION VESSEL FOR CONTROLLING THE FLOW RATIO IN SAID PARALLEL LOOPS, AND CONTROL MEANS RESPONSIVE TO THE TEMPERATURE OF THE FLUID IN SAID CONDUIT MEANS FOR MAINTAINIG THE FLUID CIRCULATING INTHE HEATING AND COOLING LOOPS AT PREDETERMINED TEMPERATURE VALUES RESPECTIVELY ABOVE AND BELOW THE TEMPERATURE OF THE FLUID ENTERING THE HEAT EXCHANGE MEANS OF THE VESSEL. 